the knot will tie itself again in a few seconds

The knot should look like this when you are done

The figure eight is a symmetrical knot that is much stonger than most knots, due to the fact that it has no sharp bends where the knot might break. It is often used to tie a rope into a harness when it is tied back on itself like a water knot. This variation of the figure eight is called a "Flemish Bend". When tied as a loop, the figure eight knot can be used with a carbiner to secure a harness to an anchor. However, a figure eight loop is only used to connect a harness to the end of a rope. If you want to tie in to the middle of a rope, you should use a butterfly knot instead.